(a) Field of the Invention
The present invention relates to a thin film transistor (TFT) array panel and a liquid crystal display (LCD) having the TFT array panel, particularly to a transmissive-reflective LCD and a TFT array panel thereof.
(b) Description of the Related Art
LCDs are one of the most widely used flat panel displays. An LCD includes a liquid crystal (LC) layer interposed between two panels provided with field-generating electrodes. The LCD displays images by applying voltages to the field-generating electrodes to generate an electric field in the LC layer that determines orientations of LC molecules in the LC layer to adjust polarization of incident light. The light having adjusted polarization is either intercepted or allowed to pass by a polarizing film, thereby displaying images.
Depending on their light sources, LCDs are classified into a transmissive LCD and a reflective LCD. The light source of the transmissive LCD is a backlight. The light source of the reflective LCD is an external light. The reflective type LCD is usually applied to a small or middle size display device.
A transmissive-reflective LCD has been under development. The transmissive-reflective LCD uses both a backlight and an external light as the light sources depending on circumstances, and usually applied to small or middle size display devices. The trans-reflective LCD includes a transmissive region and a reflective region in a pixel. While light passes through an LC layer only once in the transmissive region, light passes through the LC layer twice in the reflective region. Accordingly, gamma curves of the transmissive region and the reflective region are not coincident, and images are displayed in different ways between the transmissive region and the reflective region.
To solve the problem, the LC layer may be formed to have different thicknesses (cell gaps) between the transmissive region and the reflective region. Alternatively, the trans-reflective LCD may be driven by two different driving voltages depending on whether the LCD is in a transmissive mode or a reflective mode.
However, when the two cell gap structure is applied, a thicker layer is required to be formed on the reflective region, thereby complicating the manufacturing process. Furthermore, since a high step is formed between the transmissive region and the reflective region, the LC molecules are aligned in a disorderly manner around the high step, thereby causing disclination in an image. Also, brightness reversion may occur in a high voltage range. On the other hand, when the two different driving voltages method is applied, gamma curves can not be coincident due to the inconsistency between critical voltages for transmissive brightness and reflective brightness.